Beatlemaniacs, Beliebers, Directioners - why do they scream?

One Direction fans scream as the band takes the stage to perform during their 2012 tour.

When One Direction performs on the North American leg of their "Where We Are" tour starting tonight in East Rutherford, you'll have to squint your ears to hear the boy bands' hits amid a more ancient and fascinating sound: the emptying of adolescent lungs.

Obviously, there will be screaming — high-decibel, high-pitch swells that push hard on the eardrums and then harder, toward the surreal. It's an abstract sound that JC Chasez has had years to ponder as a member of the multi-platinum juggernaut 'N Sync. But putting the power of that communal wail into words still isn't easy.

"Sound is energy," Chasez says. "And the entire room is producing sound, not just the people onstage, so when the entire room is resonating with every human being producing, it's a very exciting feeling."

Surely. But what's behind that feeling? Why do young women assembled at pop concerts express their collective ecstasy with the most alarming sound available to their bodies? Why do they scream?

In some ways, today's young fans are simply imitating the ritualized shrieks of the generations that preceded them, from the Beatlemaniacs to the Beliebers. And while today's tween screams aren't reserved exclusively for young male heartthrobs, concerts by Miley Cyrus and Taylor Swift don't seem to generate quite the same sonic fervor as a performance from One Direction or Ed Sheeran.

Since the splashdown of Elvis Presley in 1956, the American media have often characterized the din of young female fans gathered in the presence of a pop idol as "hysteria" — "a description that denigrates their musical engagement," according to a 2003 article written by Australian researcher Sarah Baker.

'Intensely real'

"Not only do these screaming, crushing bodies animate these [performance] spaces," Baker writes, "but they also make the pop experience feel intensely real for both the girls involved and the wider public."

So when the lights go down at a 21st century boy band revue, we aren't hearing a helpless, hysteric howl.

We're hearing a complex expression of individualism and collectivity — perhaps with a dash of Darwin thrown in.

Sociologists have different names for different types of crowds. The noisy throngs at a pop concert qualify as an "expressive crowd" — a gathering in which the participants are given implicit permission to abandon decorum and freak out.

"When men cry at a sports event, it's very similar" to the screaming that takes place at a One Direction concert, says author Rachel Simmons. "It wouldn't be OK for men to do that anywhere else. But the sporting event sanctions that behavior."

Simmons is the author of "The Curse of the Good Girl," a book in which she argues that young women are unfairly asked to squeeze into an impossible mold of politeness and modesty. Simmons says a concert is a unique event that gives girls the rare opportunity to break out of those roles.

"In their day-to-day, non-concert-going lives, girls don't have a lot of permission to scream," she says. "A concert offers an oasis from the daily rules about being good girls. Screaming is about letting go and leaving the confines of being the self-conscious pleaser."

That's one way to explain why so many concerts are filled with screaming girls instead of screaming boys.

"Screaming is a way to control a situation," says Michelle Janning, a professor of sociology at Whitman College in Walla Walla, Wash. "When you're a kid, and a girl, you don't have control. Young people don't have a loud voice in society, so screaming in this kind of space is a way to have a voice. Literally."

Janning also believes that girls have felt an expectation to scream ever since Beatlemania spread across the land in 1964. "We're constantly being socialized to see crowds of girls screaming at rock stars," Janning says. "So we're following the crowd, doing what we've seen other people do. But we also want to stand out as individuals."

Both Janning and Simmons agree that concert screaming ultimately provides girls a chance to express their individuality while reinforcing their place in the larger group. And it can also be a place for competition.

Group screamers

"Adolescent girls are really invested in the acceptance of their peers," Simmons says. "But there's a competitive element to fandom and fan-girling - and screaming is an expression of that fandom. So girls are doing it not only to assert their passion for the band, but to compete with each other and to signal to each other that, 'This is what I care about.' It's part competition, but partly a way to connect. During adolescence for girls, that's a very complex and important drive."